Nine militants also lost their lives in the assaults in the desert of the southern province of Swaida, the Britain-based Syrian Observatory for Human Rights activist group said.

They were the first attacks of their kind in the area, where no Daesh presence had been noted in more than a year, Observatory head Rami Abdel-Rahman said.

The 17 pro-regime combatants killed also included nine Iranians and fighters belonging to pro-Iran Shiite militias, as well as two unidentified fighters, he said.

Daesh has ramped up its attacks against pro-regime forces since its fighters last month left their last stronghold near Damascus under an evacuation deal with the regime.

The new toll brings to 179 the number of pro-regime troops killed in more than two weeks in militant attacks across the country since May 22. At least 89 militants were killed during that same period.

Daesh in 2014 proclaimed a cross-border "caliphate" in Syria and neighboring Iraq, but has since lost most of that territory to separate offensives by Russia-backed regime troops and a U.S.-backed Kurdish-Arab alliance.

The militants now control no more than three percent of Syria, the Observatory says, mostly in the eastern desert near the border with Iraq.